Combustion-powered nailers are known in the art for driving fasteners into workpieces, and examples are described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722; 5,197,646; 5,263,439 and 5,713,313, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE® and PASLODE® brands.
Such nailers incorporate a housing enclosing a small internal combustion engine or power source. The engine is powered by a canister of pressurized fuel gas, also called a fuel cell. A battery-powered electronic power distribution unit produces a spark for ignition, and a fan located in a combustion chamber provides for both an efficient combustion within the chamber, while facilitating processes ancillary to the combustion operation of the device. Such ancillary processes include: mixing the fuel and air within the chamber, turbulence to increase the combustion process, scavenging combustion by-products with fresh air, and cooling the engine. The engine includes a reciprocating piston with an elongated, rigid driver blade disposed within a cylinder body.
A valve sleeve is axially reciprocable about the cylinder and, through a linkage, moves to close the combustion chamber when a work contact element at the end of the linkage is pressed against a workpiece. This pressing action also triggers a fuel-metering valve to introduce a specified volume of fuel into the closed combustion chamber.
Upon the pulling of a trigger switch, which causes the spark to ignite a charge of gas in the combustion chamber of the engine, the combined piston and driver blade is forced downward to impact a positioned fastener and drive it into the workpiece. The piston then returns to its original or pre-firing position, through differential gas pressures created by cooling of residual combustion gases within the cylinder. Fasteners are fed magazine-style into the nosepiece, where they are held in a properly positioned orientation for receiving the impact of the driver blade.
As the piston is displaced in the cylinder, a swept volume of air is discharged through exhaust and vent ports. Following the drive stroke, the vent ports allow atmospheric air to enter the cylinder, on the non-combustion side of the piston, and facilitate the return of the piston via differential pressures.
An operational problem of conventional combustion nailers is that as air required for combustion enters the tool, due to the relatively dirty operational environment, dirt, dust and/or other debris, including but not limited to fragments of nail collation material, sawdust, wallboard particles and the like enters the tool, specifically the cylinder below the piston. This contaminated air enters mainly through the air vent ports located below the exhaust ports as the piston returns to its pre-firing position after combustion. These air ports are typically located below or in close proximity to a shock-absorbing bumper located within the cylinder. Air cannot reenter through the exhaust ports due to the presence of one-way petal valves. Thus, these ports do not contribute to the problem. Among other effects, through prolonged tool operation, these contaminants build up to cause piston malfunctions and deterioration of tool lubricants required for smooth operation of the piston and movement of the reciprocating valve sleeve, the component used to close the combustion chamber. Thus, more frequent cleaning and/or service is required.
Such nailers typically have an air filter located at an upper end of the tool near the combustion chamber fan air intake. However, this filter has been designed to filter air entering the tool and has no effect on the air located below the piston inside the cylinder, where contaminant-caused damage has been known to occur. To address this issue, manufacturers have incorporated a dust boot or shroud over the lower end of the tool. This feature reduces direct exposure of the engine to large contaminants, but is not effective to reduce fine contaminants that enter the cylinder during the piston return cycle. Additionally, such designs are bulky and restrict air flow through the tool. Alternatively, filter elements can be used, but the fine filtration properties of effective filters are prone to clogging when located at the lower end of the nailer, and are restrictive to air flow in and out of the cylinder. Also, the size of any such filter would necessarily be relatively large to permit the passage of sufficient air to maintain proper air circulation within the tool. As such, space, material and tool operational factors combine to discourage tool designers from placing a filter on the tool to filter the air in the cylinder below the piston.
Thus, there is a need for an improved combustion tool configured for reducing the harmful effects of contaminants drawn through the cylinder vent ports, while maintaining effective air flow between the inside and outside of the cylinder.